Les faunes de foraminifères benthiques de l’Océan Arctique

Rapport pour Tota

On metal-deficient barium stars and their link with yellow symbiotic stars

This paper addresses the question of why metal-deficient barium stars are not yellow symbiotic stars (YSyS). Samples of (suspected) metal-deficient barium (mdBa) stars and YSyS have been collected from the literature, and their properties reviewed. It appears in particular that the barium nature of the suspected mdBa stars needs to be ascertained by detailed abundance analyses. Abundances are therefore derived for two of them, HD 139409 and HD 148897, which reveal that HD 148897 should not be considered a barium star. HD 139409 is a mild barium star, with overabundances observed only for elements belonging to the first s-process peak (Y and Zr). The evidence for binarity among mdBa stars is then reviewed, using three different methods: (i) radial-velocity variations (from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii) a method based on the comparison between the Hipparcos and Tycho-2 proper motions. A first-time orbit is obtained for HIP 55852, whereas evidence for the (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874 and HIP 107478 is presented. Two stars with no evidence for binarity whatsoever (HIP 58596 and BD +3 2688) are candidates low-metallicity thermally-pulsing asymptotic giant branch stars, as inferred from their large luminosities. The reason why mdBa stars are not YSyS is suggested to lie in their different orbital period distributions: mdBa stars have on average longer orbital periods than YSyS, and hence their companion accretes matter at a lower rate, for a given mass loss rate of the giant star. The definite validation of this explanation should nevertheless await the determination of the orbital periods for the many mdBa stars still lacking periods, in order to make the comparison more significant.Comment: Astronomy & Astrophysics, in press; 16 pages, 14 figures; also available at http://www.astro.ulb.ac.be/Html/ps.html#PR

A holistic approach to carbon-enhanced metal-poor stars

By considering the various CEMP subclasses separately, we try to derive, from the specific signatures imprinted on the abundances, parameters (such as metallicity, mass, temperature, and neutron source) characterizing AGB nucleosynthesis from the specific signatures imprinted on the abundances, and separate them from the impact of thermohaline mixing, first dredge-up, and dilution associated with the mass transfer from the companion.To put CEMP stars in a broad context, we collect abundances for about 180 stars of various metallicities, luminosity classes, and abundance patterns, from our own sample and from literature. First, we show that there are CEMP stars which share the properties of CEMP-s stars and CEMP-no stars (which we call CEMP-low-s stars). We also show that there is a strong correlation between Ba and C abundances in the s-only CEMP stars. This strongly points at the operation of the 13C neutron source in low-mass AGB stars. For the CEMP-rs stars (seemingly enriched with elements from both the s- and r-processes), the correlation of the N abundances with abundances of heavy elements from the 2nd and 3rd s-process peaks bears instead the signature of the 22Ne neutron source. Adding the fact that CEMP-rs stars exhibit O and Mg enhancements, we conclude that extremely hot conditions prevailed during the thermal pulses of the contaminating AGB stars. Finally, we argue that most CEMP-no stars (with no overabundances for the neutron-capture elements) are likely the extremely metal-poor counterparts of CEMP neutron-capture-rich stars. We also show that the C enhancement in CEMP-no stars declines with metallicity at extremely low metallicity ([Fe/H]~< -3.2). This trend is not predicted by any of the current AGB models.Comment: 27 pages, 24 figures, accepted for publication in A&

Towards an operational use of benthic foraminifera for organic pollution monitoring in open and enclosed marine environments: case histories from the outer shelf off Congo and the Firth of Clyde in Scotland.

Foraminifera are among the most abundant protists in marine benthic environments. Because of their short life cycles, high biodiversity and specific ecological requirements of individual species, foraminifera react quickly to environmental disturbance, and can be successfully employed as bio-indicators of environmental change, such as those brought about by anthropogenic pollution. In the last decennia, foraminifera have been increasingly used to monitor pollution in a wide range of marine environments, such as intertidal mudflats impacted by oil spillages, harbours affected by heavy metal pollution, or eutrophicated continental shelves. Our best examples of anthropogenic eutrophication are 1) a drill cutting disposal sites at the outer continental shelf off Congo, where we observed a zonation of foraminiferal faunas in the 750 m around the discharge point. In the immediate vicinity of the discharge points (within 70 m), faunas are characterised by low foraminiferal densities. Faunas between 70 m and 250 m of the disposal sites have very high foraminiferal densities, with high percentages of opportunistic taxa such as B. aculeata and B. marginata. Between 250 and 750 m, foraminiferal densities decrease, and the percentages of opportunistic species are lower; 2) a sewage sludge disposal on the sea floor in the Firth of Clyde (Scotland) where we used benthic foraminifera and macrofaunal/meiofaunal assemblages to evaluate the impact. These two communities present a very similar distributional pattern around the disposal site. In its immediate vicinity, both groups show impoverished faunas composed exclusively of species tolerant to strong oxygen depletion. This area is surrounded by an aureole of high density faunas dominated by opportunistic species. Still farther away, faunal density decreases, and equilibrium taxa gradually replace opportunistic species. At about 3 Km of the disposal site, both foraminiferal and macro-/meiofaunal taxa become comparable to those found at the reference station. We used these data to develop a quantitative pollution index, values of which are strongly correlated with the distance to the disposal site. This foraminiferal index offers the possibility to quantify the impact of anthropogenic eutrophication in marine environments, but its validity must be tested in wider range of naturally and anthropogenetically impacted marine environments.Foraminifera are among the most abundant protists in marine benthic environments. Because of their short life cycles, high biodiversity and specific ecological requirements of individual species, foraminifera react quickly to environmental disturbance, and can be successfully employed as bio-indicators of environmental change, such as those brought about by anthropogenic pollution. In the last decennia, foraminifera have been increasingly used to monitor pollution in a wide range of marine environments, such as intertidal mudflats impacted by oil spillages, harbours affected by heavy metal pollution, or eutrophicated continental shelves. Our best examples of anthropogenic eutrophication are 1) a drill cutting disposal sites at the outer continental shelf off Congo, where we observed a zonation of foraminiferal faunas in the 750 m around the discharge point. In the immediate vicinity of the discharge points (within 70 m), faunas are characterised by low foraminiferal densities. Faunas between 70 m and 250 m of the disposal sites have very high foraminiferal densities, with high percentages of opportunistic taxa such as B. aculeata and B. marginata. Between 250 and 750 m, foraminiferal densities decrease, and the percentages of opportunistic species are lower; 2) a sewage sludge disposal on the sea floor in the Firth of Clyde (Scotland) where we used benthic foraminifera and macrofaunal/meiofaunal assemblages to evaluate the impact. These two communities present a very similar distributional pattern around the disposal site. In its immediate vicinity, both groups show impoverished faunas composed exclusively of species tolerant to strong oxygen depletion. This area is surrounded by an aureole of high density faunas dominated by opportunistic species. Still farther away, faunal density decreases, and equilibrium taxa gradually replace opportunistic species. At about 3 Km of the disposal site, both foraminiferal and macro-/meiofaunal taxa become comparable to those found at the reference station. We used these data to develop a quantitative pollution index, values of which are strongly correlated with the distance to the disposal site. This foraminiferal index offers the possibility to quantify the impact of anthropogenic eutrophication in marine environments, but its validity must be tested in wider range of naturally and anthropogenetically impacted marine environments

Deep-sea benthic foraminifera faunas and stable isotopes from the Portugal margin

Abstrac

Benthic foraminifera as bio-indicators of drill cutting disposal in tropical east Atlantic outer shelf environments

We present a study of benthic foraminiferal faunas from the outer continental shelf off Congo (tropical West Africa), with the aim to determine the impact of the discharge of oily drill cuttings on the sea floor environment, to judge the regenerating capacity of the benthic ecosystem, and to investigate the possibility to develop an environmental monitoring method for open marine continental shelf environments, based on benthic foraminifera. We studied the spatial distribution and microhabitats of living and dead foraminiferal faunas, sampled in April 2003, 4 years after the end of disposal activities, in the upper 3 cm of the sediment at 9 stations (about 180 m depth) offshore Congo, that were subject to various degrees of pollution by oily cuttings from 1993 until 1999. Our results describe a zonation of foraminiferal faunas in the 750 m around the former disposal sites. At the immediate vicinity of the discharge points (within 70 m), faunas are characterized by low foraminiferal densities. Faunas between 70 m and 250 m of the disposal sites have very high foraminiferal densities, with high percentages (about 80%) of opportunistic taxa such as Bulimina aculeata, Bulimina marginata, Textularia sagittula, Trifarina bradyi and Bolivina spp. Between 250 and 750 m from the disposal site, foraminiferal densities decrease, and the percentages of opportunistic species are lower (40–60% of indicator species). These results show that 4 years after the cessation of oily cutting disposal, strong environmental impact is limited to the 250 m around the disposal sites. We used these data to develop a quantitative pollution index, values of which are strongly correlated to distance to the disposal site. This foraminiferal index offers the possibility to quantify the impact of anthropogenic eutrophication in continental shelf environments, but its validity must be tested in other continental shelf environments

Living small-sized (63-150 µm) foraminifera from mid-shelf to mid-slope environments in the Bay of Bisca

Live (rose Bengal stained) foraminiferal faunas of the 63–150 μm size fraction have been investigated in surficial sediment (0–1 cm) from mid-shelf to mid-slope environments in the Bay of Biscay. Eleven stations were sampled in April 2002 and March 2004 between 80 and 2000 m water depth (mwd). Earlier studies on the temporal variability of phytoplankton primary production suggest that our stations were sampled at the most eutrophic period of the year. In response to the decrease of exported organic matter flux to the seafloor along our bathymetric transect, foraminiferal standing stocks decrease from ~1400–2000 specimens per 50 cm3 on the continental shelf (100–140 mwd) and upper slope (550 mwd) to about 400 specimens per 50 cm3 at mid-slope stations (2000 mwd). At all stations, the faunas contain an important amount of small opportunistic species that are favored by seasonal phytodetritus input. On the continental shelf where phytoplankton bloom, events may be geographically restricted; the foraminiferal response is dependent on the distance to the surface-water primary-production cells. Textularia porrecta is very abundant at an 80-m-deep station that is close to the coast and characterized by a high sedimentation rate of fine-grained particles. Foraminiferal faunas are dominated by Nonionella iridea, Cassidulina carinata and Bolivina ex. gr. dilatata at the outer-shelf stations (110–140 mwd) that are under the direct influence of spring bloom phytodetritus input in the northern Bay of Biscay. A fauna dominated by Bolivina dilatata/spathulata and Bolivina subaenariensis is found in the southeastern Bay of Biscay at a 140-m-deep outer-shelf station located seaward of the Adour River estuary, where the sediment is probably enriched in terrestrial organic matter. Apparently, differences in foraminiferal composition between outer-shelf areas in the northern and southeastern Bay of Biscay are related to differences in organic matter quality. On the continental slope, a bathymetric zonation of taxa is observed from upper-slope sites (550–1000 mwd) rich in Epistominella exigua and Uvigerina peregrina to mid-slope stations (1600–2000 mwd), where Nuttallides pusillus and Gavelinopsis translucens dominate the small-sized living fauna. This bathymetric foraminiferal zonation probably reflects a trophic gradient between upper-slope eutrophic stations and mid-slope, more oligotrophic sites. Our zonal description of small-sized living foraminifera (63–150 μm) is new for the Bay of Biscay and may provide the basis to reconstruct former export production regimes in marginal paleo-environments from temperate latitude areas

CH in stellar atmospheres: an extensive linelist

The advent of high-resolution spectrographs and detailed stellar atmosphere modelling has strengthened the need for accurate molecular data. Carbon-enhanced metal-poor (CEMP) stars spectra are interesting objects with which to study transitions from the CH molecule. We combine programs for spectral analysis of molecules and stellar-radiative transfer codes to build an extensive CH linelist, including predissociation broadening as well as newly identified levels. We show examples of strong predissociation CH lines in CEMP stars, and we stress the important role played by the CH features in the Bond-Neff feature depressing the spectra of barium stars by as much as 0.2 magnitudes in the $\lambda=$3000 -- 5500 \AA\ range. Because of the extreme thermodynamic conditions prevailing in stellar atmospheres (compared to the laboratory), molecular transitions with high energy levels can be observed. Stellar spectra can thus be used to constrain and improve molecular data.Comment: 33pages, 15 figures, accepted in A&A external data available at http://www.astro.ulb.ac.be/~spectrotools